Structures and methods for electrically connecting printed horizontal components

ABSTRACT

A printed structure comprises a device comprising device electrical contacts disposed on a common side of the device and a substrate non-native to the device comprising substrate electrical contacts disposed on a surface of the substrate. At least one of the substrate electrical contacts has a rounded shape. The device electrical contacts are in physical and electrical contact with corresponding substrate electrical contacts. The substrate electrical contacts can comprise a polymer core coated with a patterned contact electrical conductor on a surface of the polymer core. A method of making polymer cores comprising patterning a polymer on the substrate and reflowing the patterned polymer to form one or more rounded shapes of the polymer and coating and then patterning the one or more rounded shapes with a conductive material.

PRIORITY APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 63/050,732, filed on Jul. 10, 2020, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure relates generally to structures and methods forelectrically connecting devices (e.g., printed devices) to destinationsubstrates.

BACKGROUND

Electronic systems typically comprise a substrate, for example abackplane, such as a printed circuit board, on which are assembledelectronic components such as integrated circuits, resistors capacitors,inductors, and connectors. The electronic components can be surfacemount devices (SMDs) that are typically placed on the backplane togetherwith solder bumps using mechanical pick-and-place equipment and thenheated to reflow the solder, thereby adhering the electronic componentsto the backplane and electrically connecting the electronic componentsto contact pads or other electrical conductors on the backplane. Atpresent, the smallest surface mount components have dimensions of 600 μmby 300 μm and, for very small and simple electronic devices such asresistors, dimensions of 400 μm by 200 μm. The size of the electricalconnection and spacing between contact pads or pins of the electronicdevices likewise has a lower limit, for example small solder bumps canhave a diameter of 75-150 μm and in extreme cases, solder bumps as smallas 30 μm in diameter have been tried. However, there is a demand forincreasing electronic system miniaturization with even smallerelectronic components and electrical connections.

Methods for transferring active small components, for example componentshaving a size less than the smallest surface mount devices, from onesubstrate to another are described in U.S. Pat. No. 7,943,491. Inexamples of these approaches, small integrated circuits are formed on anative semiconductor source wafer. The small unpackaged integratedcircuits, or chiplets, are released from the native source wafer byetching a layer formed beneath the circuits. A PDMS stamp is pressedagainst the native source wafer and the process side of the chiplets isadhered to individual stamp posts. The chiplets are removed from thenative source wafer and pressed against a destination substrate orbackplane with the stamp to adhere the chiplets to the destinationsubstrate.

In other examples, U.S. Pat. No. 8,722,458 teaches transferringlight-emitting, light-sensing, or light-collecting semiconductorelements from a wafer substrate to a destination substrate or backplane.The chiplets are then electrically connected using conventionalphotolithographic methods (e.g., forming patterned metal wires usingblanket metal evaporation and photoresist coating, patterned maskexposure, cure, pattern-wise etching, and photoresist stripping).However, these steps can be slow, complex, and relatively expensive forcertain applications.

There remains a need, therefore, for disposing small electroniccomponents on a backplane (or other substrates) and electricallyconnecting the small electronic components to conductors (e.g., contactpads or wires) formed on the backplane.

SUMMARY

The present disclosure provides, inter alia, structures, materials, andmethods that provide electrical connections between small electroniccomponents (e.g., having at least one of a length and a width no greaterthan 200 μm) disposed on a substrate, for example by transfer printing(e.g., micro-transfer printing).

According to some embodiments of the present disclosure, a printedstructure comprises a device comprising device electrical contactsdisposed on a common side of the device and a substrate non-native tothe device comprising substrate electrical contacts disposed on asurface of the substrate. At least one of the substrate electricalcontacts has a rounded shape. The device electrical contacts are inphysical and electrical contact with the corresponding substrateelectrical contacts (e.g., each of the device electrical contacts is incontact with a corresponding substrate electrical contact of thesubstrate electrical contacts). The rounded shape can be at least aportion of a sphere, a portion of a hemisphere, or have one or more sidewalls with a first curvature and a top with a second curve that has alarger curvature than the first curve, e.g., a flattened top on anopposite side of the rounded shape from the substrate.

According to some embodiments, the device electrical contacts aresubstantially planar and are disposed in a common plane. According tosome embodiments, the device electrical contacts are substantiallyplanar and are disposed in different planes (e.g., each in its ownplane). Each of the at least one of the substrate electrical contactscan conform to the shape of a corresponding device electrical contact ofthe device electrical contacts and a contact electrical conductor on asubstrate electrical contact can wick along the device electricalcontact.

According to some embodiments of the present disclosure, at least one ofthe substrate electrical contacts having a rounded shape comprises apolymer core coated with a contact electrical conductor on a surface ofthe polymer core. The polymer core can be compliant, conformal,flexible, or reflowable. The polymer core can be soft cured, reflowed,and then hard cured. The polymer core can comprise an electricallyconductive polymer. The contact electrical conductor can be anelectrically conductive surface layer that comprises a metal, a metalalloy, a solder, a transparent conductive oxide, or an electricallyconductive polymer. The contact electrical conductor can be reflowableand can wick along another electrically conductive surface. The contactelectrical conductor comprising a conductive surface layer can have athickness no more than 25% of a lateral extent of the polymer core overthe surface of the substrate. The conductive surface layer can have athickness of no more than 250 nm. The contact electrical conductor canbe, is, or has been wicked along the device electrical contact.According to some embodiments, each of the at least one of the substrateelectrical contacts has a lateral extent over the substrate of no morethan 10 μm.

According to some embodiments of the present disclosure, the devicecomprises one or more active layers through which current flows whencurrent is provided from the substrate electrical contacts through thedevice electrical contacts. According to some embodiments, the device istilted with respect to the destination substrate. According to someembodiments, the substrate electrical contacts are at least partiallytransparent to visible light or light emitted by the device, e.g., atleast 50 percent transparent. According to some embodiments, the deviceis a light-emitting diode, an inorganic light-emitting diode, or anorganic light-emitting diode. According to some embodiments, the devicehas a surface of a second side opposite the common side and the surfaceof the second side is roughened.

According to some embodiments of the present disclosure, the substrateis an intermediate substrate and the printed structure further comprisesa system substrate comprising substrate conductors disposed on or in thesystem substrate. The device is electrically connected to the substrateconductors through the substrate electrical contacts. Printed structuresof the present disclosure can comprise a second device comprising seconddevice electrical contacts disposed on a common side of the seconddevice, wherein the substrate further comprises second substrateelectrical contacts disposed on the surface of the substrate and whereinat least one of the second substrate electrical contacts has a roundedshape and each of the second device electrical contacts is in electricaland physical contact with one of the second substrate electricalcontacts. The substrate electrical contacts can be electricallyconnected to one or more substrate conductors disposed in or on thesubstrate.

According to some embodiments of the present disclosure, the device hasat least one of a width, a length, and a thickness of no more than 100μm, or the device has a length to width ratio of at least 1:1, 2:1, or4:1, and/or the device has a length and/or width to thickness aspectratio of at least 1:1, 2:1, 5:1, or 10:1.

According to some embodiments of the present disclosure, printedstructures can comprise an adhesive disposed between the device and thesubstrate that adheres the device to the substrate. The adhesive canhave a higher Young's modulus than at least one of the substrateelectrical contacts. The adhesive can be cured, soft cured, or hardcured. The adhesive can be or can be in an unpatterned adhesive layer.The adhesive can be a patterned layer. The adhesive can have a thicknessless than a thickness of at least one of the substrate electricalcontacts such that each of the at least one of the substrate electricalcontacts protrudes above the adhesive. At least one of the substrateelectrical contacts can have a thickness or height that is greater thana distance between surfaces of ones of the device electrical contacts ina direction orthogonal to at least one of the surfaces. In suchembodiments, ones of the device electrical contacts can be disposed indifferent planes.

According to some embodiments of the present disclosure, all of thesubstrate electrical contacts have rounded shapes. According to someembodiments of the present disclosure, the at least one of the substrateelectrical contacts is a plurality of the substrate electrical contactsand the plurality comprises ones of the substrate contacts havingdifferent heights or sizes (e.g., thicknesses). According to someembodiments of the present disclosure, the device is an unpackaged baredie.

According to embodiments of the present disclosure, a method of makingelectrical connections comprises providing a substrate comprisingsubstrate electrical contacts disposed on a surface of the substrate,wherein at least one of the substrate electrical contacts has a roundedshape, providing a device comprising device electrical contacts disposedon a common side of the device, and printing the device to thedestination substrate such that each of the device electrical contactsis in electrical contact with one of the substrate electrical contacts.

Providing the substrate comprising substrate electrical contactsdisposed on a surface of the destination substrate can compriseproviding a substrate, patterning a polymer on the substrate, heating(e.g., reflowing) the patterned polymer to form one or more roundedshapes of the polymer, and coating (and optionally patterning) the oneor more rounded shapes with a conductive material, wherein each of theat least one of the substrate electrical contacts comprises one of theone or more rounded shapes coated with the conductive material to form aconductive surface layer that is a contact electrical conductor.According to some embodiments, coating the one or more rounded shapeswith the conductive material comprises depositing a layer of theconductive material and patterning the layer such that the one or morerounded shapes remain coated with the conductive material.

According to some embodiments, methods of the present disclosurecomprise disposing adhesive on the destination substrate prior toprinting the device, wherein printing the device comprises contactingthe device to the adhesive.

According to some embodiments, methods of the present disclosurecomprise curing the adhesive after the device has been printed.

According to some embodiments, methods of the present disclosurecomprise baking the device and the destination substrate.

According to some embodiments, methods of the present disclosurecomprise reflowing the conductive material.

According to some embodiments, methods of the present disclosurecomprise reflowing the rounded shape.

According to some embodiments, methods of the present disclosurecomprise conforming the substrate electrical contact to the deviceelectrical contact.

Embodiments of the present disclosure provide methods and structures forelectrically connecting small electronic devices to a substrate usingefficient and inexpensive manufacturing techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross section of a device comprising device electricalcontacts in a common plane printed onto a substrate with roundedcontacts, according to illustrative embodiments of the presentdisclosure;

FIG. 2 is a cross section of a tilted horizontal LED comprising deviceelectrical contacts in different planes printed onto a substrate withrounded contacts, according to illustrative embodiments of the presentdisclosure;

FIG. 3 is a cross section of a horizontal LED with a roughened surfaceand comprising device electrical contacts in different planes printedonto a substrate with rounded contacts of different sizes, according toillustrative embodiments of the present disclosure;

FIG. 4 is a cross section of multiple horizontal LEDs with roughenedsurfaces printed onto a substrate in contact with two rounded contactswhere the devices are tilted, according to illustrative embodiments ofthe present disclosure;

FIGS. 5A and 5B are each a cross section of an LED printed onto asubstrate in contact with one rounded contact and one planar contact,according to illustrative embodiments of the present disclosure;

FIGS. 6-8 are flow diagrams of methods for printing and electricallyconnecting a device, according to illustrative embodiments of thepresent disclosure;

FIGS. 9A-9H are successive cross sections illustrating methods of makinga printed structure according to illustrative embodiments of the presentdisclosure;

FIGS. 10A-10D are successive cross sections illustrating methods ofadhering a printed device to make a printed structure according toillustrative embodiments of the present disclosure;

FIG. 11 is a cross section of an LED printed onto a substrate in contactwith a conformal rounded contact according to illustrative embodimentsof the present disclosure;

FIG. 12 is plan schematic view of a display comprising printedstructures according to illustrative embodiments of the presentdisclosure;

FIG. 13 is a cross section of a pixel with a pixel substrate accordingto illustrative embodiments of the present disclosure;

FIG. 14 is a cross section of pixels of FIG. 13 on a display substrateaccording to illustrative embodiments of the present disclosure; and

FIG. 15 is a plan view of a display comprising pixels according toillustrative embodiments of the present disclosure.

Features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The figures are not necessarilydrawn to scale.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Structures and methods of embodiments of the present disclosure enableelectrically connecting printed devices, such as light-emitting devicesincluding inorganic light-emitting diodes, to substrate electricalcontacts disposed on a substrate. Each device likewise comprises adevice electrical contact. One or more substrate electrical contacts cancomprise a heat-reflowable material (such as a polymer, resin, epoxy, orsoft metal, for example) disposed on and protruding from a surface of asubstrate and coated with a surface conductive layer and patterned toform a contact electrical conductor. Substrate electrical contacts canhave a rounded shape (e.g., can be bumps, can be hemispherical, can haveother rounded shapes, or can have contact angles less than 180 degrees)and can be formed by heating (e.g., reflowing) a patterned layer ofpolymer so that surface energy (surface tension or capillary) forcesform rounded shapes at a high resolution to which devices can be printedand electrically connected without using photolithographic methods toform electrical connections between the device and the substrate. Inparticular, according to some embodiments of the present disclosure,photolithographic processing to form electrical connections between asubstrate and a printed device can be unnecessary (reducingphotolithographic processing steps) and problems with forming electricalconnections over the device edge (e.g., a step height) are avoided.

The patterned electrical conductor coating (the contact electricalconductor) can also be heat reflowable (e.g., comprise a solder). Adevice can be printed to a substrate (e.g., using an elastomeric stampto micro-transfer print the device, for example as described in U.S.patent application Ser. No. 16/532,591, filed Aug. 6, 2019, thedisclosure of which is hereby incorporated by reference herein in itsentirety) with each device electrical contact in electrical (e.g., andphysical) contact with a corresponding substrate electrical contact.After the device is printed, substrate electrical contacts can beheated, for example by heating the substrate. The heat can cause theheat-reflowable material to flow, which can cause substrate electricalcontact(s) to conform with the shape of the device electrical contact(s)and the contact electrical conductor to wick along the device electricalcontact(s) to improve electrical contact by increasing the contact areabetween the device electrical contact and the substrate electricalcontact and to firmly adhere the device to the substrate. Thus, in someembodiments, a substrate electrical contact is conformable and conformsto a device electrical contact. In some embodiments, the substrateelectrical contact can be cured after conforming to the deviceelectrical contact. A substrate electrical contact can be compliant. Theprinted structure can then be cooled, for example to room temperature,integrated into an electrical system, and operated.

As shown in FIG. 1, a printed structure 99 comprises a device 20comprising device electrical contacts 22 disposed on a common side 23 ofdevice 20 and a substrate 10 non-native to device 20 comprisingsubstrate electrical contacts 30 disposed on a surface 11 of substrate10. At least one of substrate electrical contacts 30 has a roundedshape. Common side 23 of device 20 can be adjacent to surface 11 so thatdevice electrical contacts 22 face substrate electrical contacts 30.Device electrical contacts 22 are in physical and electrical contactwith corresponding substrate electrical contacts 30. Device 20 can beany functional device, for example an electrical or optical device suchas an integrated circuit and can comprise active components (e.g.,transistors, diodes, inorganic light-emitting diodes, organiclight-emitting diodes, or sensors) and passive components (e.g.,electrical conductors such as wires, optical conductors such as lightpipes, electrical resistors, electrical capacitors, and electricalinductors). Device 20 can be electrically insulated by patterneddielectric structure 24 that exposes device electrical contacts 22.Device 20 can comprise one or more active layers (e.g., semiconductorlayers, for example forming one or more quantum wells) through whichelectrical current flows when electrical current is provided by deviceelectrical contacts 22. Device 20 can comprise one or more of a devicesubstrate (e.g., a dielectric substrate or a semiconductor substrate),patterned dielectric structures 24, and semiconductor structures orlayers (e.g., silicon or compound semiconductors). Device 20 cancomprise a semiconductor component disposed on a dielectric devicesubstrate or a semiconductor layer of device 20 can comprise a devicesubstrate. Device 20 can comprise multiple components, such as opticalor electrical components or a combination of one or more optical and oneor more electrical components (e.g., an LED and a controller). Device 20can be or comprise one or more of one or more inorganic or organiclight-emitting diodes, one or more control circuits, and one or moreelectrical conductors. Device 20 can comprise a silicon device substratewith a control circuit disposed in or on the silicon device substrateand light-emitting diodes or other compound semiconductor devicesdisposed on the silicon device substrate, for example by micro-transferprinting, that can be controlled by the control circuit. In someembodiments, a control circuit is disposed on a dielectric devicesubstrate, for example by micro-transfer printing.

Embodiments of the present disclosure can be applied to high-resolutionand dense micro-circuits with small devices 20. According to someembodiments, device 20 is a micro-device and has at least one of alength and a width no greater than 200 μm (e.g., no greater than 100 μm,no greater than 50 μm, no greater than 20 μm, no greater than 10 μm, orno greater than 5 μm). Device 20 can have various aspect ratios, forexample (i) a length to width and/or (ii) a length and/or width tothickness aspect ratio of at least 1:1, at least 2:1, at least 4:1, atleast 8:1, or at least 10:1.

Device 20 can be a flip chip, with active components provided on commonside 23 and disposed in an inverted configuration with respect tosubstrate 10. In some embodiments, device 20 comprises active componentsprovided on a side of device 20 opposite common side 23. Activecomponents can be connected to device electrical contacts 22 using, forexample vias such as through-silicon vias (TSVs). Active components indevice 20 can be formed in or on a surface of a semiconductor devicesubstrate or disposed on a semiconductor or dielectric device substrate.Components can be disposed on device 20 substrate by micro-transferprinting and can comprise fractured or separated component tethers as aconsequence of transfer printing (not shown). Moreover, devices 20 canbe micro-transfer printed onto substrate 10, for example usingelastomeric stamps, and can comprise a fractured or separated devicetether 26 as a consequence of transfer printing.

Device 20 can have two or more device electrical contacts 22. The two ormore device electrical contacts 22 can be substantially planar and canbe disposed in a common plane on common side 23, for example as shown inFIG. 1, and can be electrically connected to components in device 20.Device electrical contacts 22 can comprise a patterned metal contact pador patterned transparent conductive oxide contact pad. Device 20, deviceelectrical contacts 22, and dielectric structures 24 can be constructedusing photolithographic methods and materials, for example as found inthe integrated circuit and display industries.

Device electrical contacts 22 and substrate conductors 12 (e.g., wires)can comprise metals such as aluminum, gold, or silver or combinations(e.g., alloys) thereof and can be deposited, for example by evaporationor sputtering, and, in some embodiments, patterned using pattern-wiseexposed, cured, and etched photoresists, e.g., constructed usingphotolithographic methods and materials, imprinting methods andmaterials, or inkjet printers and materials, for example comprisingcured conductive inks deposited on a surface or provided inmicro-channels.

Substrate 10 can be any suitable substrate, for example comprising anyone or more of glass, polymer, ceramic, sapphire, quartz, or asemiconductor, having surface 11 suitable for forming substrateelectrical contacts 30 and contacting device 20, for example asubstantially planar surface (excluding rounded substrate electricalcontacts 30) within the limitations of a manufacturing process.Substrate 10 can be a backplane, a pixel substrate, a display substrate,or a printed circuit board. Substrate 10 can be patterned with substrateconductors 12, such as wires or traces, that for example, may beelectrically connected and disposed to be used to conduct electricalcurrent, ground, or electrical control signals. Conductors 12 can bedisposed in or on substrate 10. Substrate 10 can be constructed usingmethods and materials known in the integrated circuit and displayindustries.

Substrate electrical contact 30 can have a rounded shape that is atleast a portion of a sphere, ellipsoid, teardrop, or hemisphere, a solidwith an oval or elliptical cross section, that has no sharp angles orcorners, or that has one or more side walls with a first curvature and atop with a second curve that has a larger curvature than the firstcurvature (e.g., a flattened sphere with a flat or flatter portiondisposed on the top of substrate electrical contact 30). When substrateelectrical contact 30 has a rounded shape, substrate electrical contact30 is proud of (e.g., is above, protrudes from, or extends from)substrate 10 and can have a contact angle with respect to substrate 10that is no greater than 180 degrees. According to some embodiments, atleast one of substrate electrical contacts 30 conforms to the shape of acorresponding device electrical contact 22. For example, a flat portionof substrate electrical contact 30 can conform to and follow thecontours of a portion of a substantially planar device electricalcontact 22.

According to some embodiments of the present disclosure, and as shown inFIG. 1, at least one of the rounded substrate electrical contacts 30comprises a polymer core 32 coated with a patterned conductive surfacelayer forming a contact electrical conductor 34. Polymer core 32 can berigid or can be compliant, conformal, flexible, or reflowable. Forexample, polymer core 32 can be a partially cured, compliant polymer (ora softened polymer, such as one at a temperature above its glasstransition temperature) that is placed into contact with device 20 anddevice electrical contacts 22 to conform substrate electrical contacts30 to device electrical contacts 22 and then subsequently hard-cured toform a rigid polymer core 32 that conforms to device electrical contact22. Polymer core 32 can comprise an electrically conductive polymer(e.g., polythiophene or other electrically conductive polymers) and canconduct electrical current. Polymer core 32 can be photoactive andpatternable using photolithographic methods and materials. Polymer core32 can be a thermoplastic material or a thermoset material.

Contact electrical conductor 34 comprises a conductive material that canbe coated on a non-conductive core. For example, contact electricalconductor 34 can be a surface layer film comprising a thin film ofphysically deposited metal or conductive oxide, or a combination ofthese. An electrical conductor can be coated (e.g., deposited) andpatterned such that the outer surface of each polymer core 32 isseparately electrically conductive. Contact electrical conductor 34 canbe in electrical and physical contact with device electrical contact 22.Contact electrical conductor 34 (or device electrical conductor 22, orboth) can comprise a metal, a metal alloy, a solder, a transparentconductive oxide (e.g., indium tin oxide or aluminum zinc oxide), or anelectrically conductive polymer. According to some embodiments, contactelectrical conductor 34 is transparent, polymer core 32 is transparent,and substrate electrical contact 30 is transparent (or device electricalconductor 22, or both), for example 50% transparent to visible light orlight emitted from device 20 (e.g., not less than 70% transparent, notless than 80% transparent, or not less than 90% transparent to visiblelight or light emitted from device 20). Contact electrical conductor 34can be reflowable and, in some embodiments, can wick along deviceelectrical contact 22 by heating once device 20 has been printed tosubstrate 10. For example, heat can be applied to cure polymer core 32and contact electrical conductor 34 that causes polymer core 32 toreflow (e.g., soften and morphologically equilibrate) such that itconforms to device 20 and device electrical contact 22. In someembodiments, heating can alternatively or additionally cause contactelectrical conductor 34 to reflow and wick along the surface of deviceelectrical contact 22, thereby improving and strengthening the physicaland electrical contact between substrate electrical contact 30 anddevice electrical contact 22 and between substrate 10 and device 20. Byreflowing a conductive surface layer of substrate electrical contact(s)30, contact with device electrical contacts 22 can be improved,especially for device electrical contacts 22 in different planes wherecontact area between substrate electrical contacts 30 and deviceelectrical contacts 22 can be small initially (e.g., after printingprior to heating). Contact electrical conductor 34 can be a surfacelayer. As an example, in some embodiments, contact electrical conductors34 have a thickness no more than 25% of a lateral extent of polymer core32 over surface 11 of substrate 10. As another example, contactelectrical conductors 34 can have a thickness of no more than one μm(e.g., no more than 500 nm, no more than 250 nm, or no more than 100nm).

According to embodiments of the present disclosure, printed structure 99can provide devices 20 electrically connected to substrate conductors 12in a dense configuration and at a high resolution over substrate 10, forexample by micro-transfer printing devices 20 using a stamp that has atleast hundreds, at least thousands, at least tens of thousands, or atleast hundreds of thousands of posts that each pick up a respectivedevice 20 from a source wafer. Substrate conductors 12 can be wires andcan be deposited and patterned in a common step with contact electricalconductors 34. If substrate 10 is a backplane, contact electricalconductors 34 can be electrically connected to backplane wiring levelsthrough a via using traditional routing techniques.

According to some embodiments, substrate electrical contacts 30 have alateral extent (e.g., diameter 35) over substrate 10 of no more than 50μm, no more than 20 μm, no more than 10 μm, or no more than 5 μm.Furthermore, substrate electrical contacts 30 can be disposed close toeach other at a high resolution, for example separated by separationdistance 38 of no more than 50 μm, no more than 20 μm, no more than 10μm, or no more than 5 μm. Substrate electrical contacts 30 can protrudeorthogonally from surface 11 of substrate 10 to a similar distance ofheight 36 (e.g., have similar thicknesses), for example to a height 36of (e.g., have a thickness of) no more than 50 μm, no more than 20 μm,no more than 10 μm, or no more than 5 μm. For example, height 36 can be0.5 to 5 μm or 1-2 μm, diameter 35 can be 2 to 10 μm or 3-5 μm, planarelectrical contacts can be 5-10 μm wide and/or long, and device 20 canhave a length and/or width of 2-20 μm, for example 3-5 μm.

FIG. 1 illustrates a device 20 with substantially planar deviceelectrical contacts 22 disposed substantially in a common plane.According to embodiments of the present disclosure, and as shown in FIG.2, device 20 can comprise a device 20 comprising substantially planardevice electrical contacts 22 disposed on common side 23 of device 20but in different planes. The different planes can be, but are notnecessarily, substantially parallel (e.g., to within 10 degrees). Adevice 20 having multiple device electrical contacts 22 on a common side23 is a horizontal device. For example, device 20 can be a horizontalinorganic light-emitting diode. In embodiments in which substrateelectrical contacts 30 have a common height 36 and device electricalcontacts 22 are in different planes, device 20 disposed on substrate 10can be tilted with respect to surface 11 of substrate 10, for example asshown in FIG. 2. A tilted arrangement can be one in which a majorsurface of device 20 is not substantially parallel to surface 11, forexample a surface of device 20 on an opposite side of device 20 fromdevice electrical contacts 22 or substrate 10. As shown in FIG. 3, andaccording to some embodiments of the present disclosure, substrateelectrical contacts 30 on a substrate 10 can have different sizes, forexample different lateral extents over (e.g., diameters 35) or differentheights 36 above surface 11 of substrate 10. In some such embodiments,devices 20 with device electrical contacts 22 in different planes canhave a major surface that is parallel to surface 11, as also shown inFIG. 3.

According to some embodiments of the present disclosure and as shown inFIG. 3, device 20 is or comprises a light-emitting diode and a surfaceof device 20, e.g., a second side 25 surface opposite common side 23 anda surface of second side 25 is roughened. Roughening can beaccomplished, for example, by exposure to a plasma such as an oxygenplasma and the roughened surface can at least partially mitigate oreliminate total internal reflection of light emitted by active layers inthe light-emitting diode, thereby improving the efficiency, appearance,and angular distribution of light emission from the light-emittingdiode, for example to widen the angle of view for emitted light, asillustrated in FIG. 3, or compensate for a tilted light-emitting diode,as illustrated in FIG. 2.

Furthermore, for light-emitting devices, a roughened second side 25opposite device electrical contacts 22 provides a diffuse light outputthat is not dependent on the orientation angle of device 20 with respectto the substrate 10.

As shown in FIG. 4. and according to embodiments of the presentdisclosure, multiple devices 20 can be disposed on and in physical andelectrical contact with multiple corresponding substrate electricalcontacts 30 on a substrate 10. Devices 20 can be arranged randomly oversubstrate 10, in an unstructured arrangement over substrate 10 or in astructured arrangement over substrate 10 (e.g., in an array oversubstrate 10). Some devices 20 can be electrically connected togetherthrough substrate electrical conductors 30, for example by substrateconductors 12. The arrangement of devices 20 can form a display ordetector (or a combination display and detector).

According to some embodiments, and as shown in FIG. 4, substrate 10 canhave a rounded substrate electrical contact 30 provided for each deviceelectrical contact 22. In some embodiments, and as shown in FIGS. 5A and5B, a substrate 10 comprises a planar electrical contact 16 and a deviceelectrical contact 22 is in electrical (e.g., and physical) contact withplanar electrical contact 16. As shown in FIGS. 5A and 5B, devices 20have multiple device electrical contacts 22 and less than all of thedevice electrical contacts 22 are electrically connected to substrateconductors 12 through rounded substrate electrical contacts 30. Asshown, some device electrical contacts 22 can be electrically connectedto substrate conductors 12 through substantially planar electricalcontacts 16 (electrical contact pads on substrate 10) that can beelectrically connected to substrate conductors 12. Devices 20 can betilted, as shown in FIG. 5A or can be flat (not tilted), as shown inFIG. 5B, for example if substrate electrical contact 30 has a height 36substantially equal to the orthogonal difference between the differentdevice electrical contact 22 planes.

As shown in the flow diagram of FIG. 6 and with reference to thesuccessive structures illustrated in FIGS. 9A-9H, embodiments of thepresent disclosure can be constructed by providing a substrate 10 instep 100, as shown in FIG. 9A. As shown in FIG. 9B, substrate 10 iscoated with a polymer 31 (e.g., an unpatterned reflowable layer ofpolymer 31 disposed by slot coating, spin coating, or spray coating) instep 110. Polymer 31 can optionally be partially cured (e.g., softcured) and can be patterned in step 120 as shown in FIG. 9C, for exampleby coating with a photomask, exposing the photomask with a pattern,etching masked or unmasked portions of polymer 31 to form a patternedlayer of polymer 31, and stripping the photomask, as is known inphotolithography. In step 130 and as shown in FIG. 9D, patterned polymer31 can be heated with heat 80 to reflow polymer 31. Because of therelative surface energies of polymer 31 and surface 11 of substrate 10,reflowing polymer 31 can form droplets (beads) on surface 11 to formpolymer cores 32 in a rounded shape. Polymer cores 32 can then be hardcured or a hard cure can be performed later. Polymer 31 can comprise,for example, a thermoplastic material. Optionally, substrate 10 can beinitially coated with a material selected to provide a suitable surfaceenergy and enhance or enable the formation of rounded polymer cores 32.Substrate 10 and polymer cores 32 can then be coated with an electricalconductor coating 33 as shown in FIG. 9E (e.g., by evaporation,sputtering, or vapor deposition) in step 140 and patterned in step 150,as shown in FIG. 9F, to form contact electrical conductor 34 andsubstrate conductors 12 (and any planar electrical contacts 16 shown inFIGS. 5A and 5B). Surface 11 of substrate 10 is then coated withadhesive 40 in step 160 as shown in FIG. 9G. Substrate electricalcontact 30 can have or be treated to have a surface energy selected toreduce the amount of adhesive 40 that coats substrate electrical contact30. Devices 20 with device electrical contacts 22 are provided in step170 and disposed (e.g., micro-transfer printed) onto substrateelectrical contacts 30 in step 180 and as shown in FIG. 9H. Adhesive 40is cured in step 190 to form printed structure 99. The resulting printedstructure 99 comprises a mass-transferred device 20 that is mechanicallyattached to substrate 10 through the cured polymer resin adhesive 40,like a die attach, and the same device 20 is electrically connected tothe underlying backplane (substrate 10) through the physical bondbetween the underside device electrical conductor 22 (device contactpad) and the substrate electrical conductor 30 (substrate contactelectrical conductor 34 or substrate contact pad disposed on thetop-side conductive surface layer of polymer core 32 in a roundedconfiguration such as a bump).

In some embodiments, device electrical contacts 22 are brought intophysical and electrical contact with contact electrical conductors 34 bymicro-transfer printing, for example as shown in FIG. 9H. In someembodiments, adhesive 40 can be disposed between device electricalcontacts 22 and contact electrical conductors 34. In either case, curingadhesive 40 shrinks adhesive 40 and pulls device 20 toward substrate 10so that device electrical contacts 22 are brought more closely intophysical and electrical contact with contact electrical conductor 34 andsubstrate electrical contacts 30. Polymer core 32 of substrateelectrical contacts 30 can have a lower Young's modulus than adhesive40. According to some methods of the present disclosure, and asillustrated in the flow diagram of FIG. 7 and in FIG. 9G, a relativelythin layer of adhesive 40 is disposed over substrate 10 in step 162 thathas a depth less than height 36 of substrate electrical contacts 30.When devices 20 are transfer printed (e.g., micro-transfer printed withan elastomeric stamp) in step 180, a portion of devices 20 contactsadhesive 40 and, when adhesive 40 is cured and shrinks in step 190,devices 20 are brought into closer proximity to substrate 10 and deviceelectrical contacts 22 are brought into closer proximity and electricalcontact with substrate electrical contacts 30. Optionally, contactelectrical conductor 34 of substrate electrical contacts 30 reflows towick onto device electrical contact 22 to improve electrical contactwith device electrical contact 22 when heated (e.g., during an adhesivecuring step). In some embodiments, device electrical contact 22comprises reflowable material, such as a solder that wicks onto contactelectrical conductor 34 (or both). In some embodiments, reflowing aconductor (whether from device electrical contact 22 or substrateelectrical contact 30) can occur as a part of curing adhesive 40.Similarly, in some embodiments, polymer core 32 can reflow and conformto or comply with device electrical contact 22 as a part of curingadhesive 40.

According to some methods of the present disclosure, and as shown inFIG. 10A, a relatively thick layer of adhesive 40 is disposed oversubstrate 10 that has a depth greater than height 36 of substrateelectrical contacts 30. If devices 20 are transfer printed (e.g.,micro-transfer printed with an elastomeric stamp) in step 180 onto sucha thick adhesive 40 layer, devices 20 can be disposed on (e.g., floaton) adhesive 40 (although in some embodiments adhesive 40 is pushedaside and device electrical contacts 22 are disposed in contact withsubstrate electrical contacts 30). In some embodiments, curing adhesive40 can bring device electrical contacts 22 into physical and electricalcontact with substrate electrical contacts 30, as described above withrespect to FIG. 7. Adhesive 40 is then cured in step 190.

According to some methods of the present disclosure, and as illustratedin the flow diagram of FIG. 8 and successive cross sections of FIGS.10A-10D, a relatively thick layer of adhesive 40 is disposed oversubstrate 10 in step 164 that has a depth greater than height 36 ofsubstrate electrical contacts 30, as shown in FIG. 10A. Adhesive 40 ispartially cured (e.g., soft cured) in step 166 and patterned in step168, as shown in FIG. 10B. Devices 20 are transfer printed (e.g.,micro-transfer printed with an elastomeric stamp) in step 180 anddisposed on adhesive 40 (e.g., float on adhesive 40) as shown in FIG.10C. In some such embodiments, when adhesive 40 is heated or cured,adhesive 40 reflows and spreads over local portions of substrate 10 instep 192 so that devices 20 are brought into closer proximity tosubstrate 10 and device electrical contacts 22 are brought into closerproximity and electrical contact with substrate electrical contacts 30,as shown in FIG. 10D. Adhesive 40 is then cured in step 190. The curestep 190 can be done in stages so as to initially reflow polymer core 32as in step 130 to conform to device electrical contacts 22 and wickcontact electrical conductor 34 in step 194 and then finally to hardcure adhesive 40 and polymer core 32.

Adhesive 40 can comprise a layer of resin, polymer, or epoxy, eithercurable or non-curable and can be disposed, for example by coating orlamination as an unpatterned layer or a patterned layer. In someembodiments, the layer of adhesive 40 is disposed in a pattern, forexample using inkjet, screen printing, or photolithographic techniques.In some embodiments, a layer of adhesive 40 is coated, for example witha spray or slot coater, and then patterned, for example usingphotolithographic techniques.

According to some embodiments of the present disclosure and asillustrated in FIG. 11, substrate electrical contacts 30 can conform todevice electrical contacts 22 after device 20 is transfer printed tosubstrate 10, for example by heating. For example polymer core 32 canreflow (for example when heated can reflow, soften, and conform todevice electrical contact 22 as a consequence of surface tension andrelative surface energies, e.g., capillary forces), and then be hardcured (e.g., baked) to permanently set polymer core 32 into a conformalconfiguration. Contact electrical conductor 34 can also reflow whenheated and the material can wick along a surface of device electricalcontact 22 and then harden when the printed structure 99 is cooled.According to some embodiments of the present disclosure, polymer 31layer is soft-baked (heated to a lower temperature), cooled, patternedusing photolithography, and then reheated to reflow the patternedpolymer 31 to form polymer cores 32. After transfer printing device 20,polymer cores 32 are again heated, together with any adhesive 40, toconform polymer cores 32 to device 20 and device electrical contacts 22and wick contact electrical conductor 34 along device electricalcontacts 22. Printed structure 99 is then cooled for use.

According to embodiments of the present disclosure, and as illustratedin FIG. 12, pixels 60 in a display 50 can comprise printed structures99, for example in an active-matrix-controlled array. Substrate 10 ofprinted structures 99 can be common to all printed structures 99 (e.g.,as in FIG. 4) and can be a display substrate 62. Each pixel 60 (andprinted structure 99) can be controlled through row wires 56 and columnwires 58 (e.g., substrate conductors 12) connected to a row controller52 and a column controller 54, respectively. Row controller 52 andcolumn controller 54 can be driven through buses 70 from a displaycontroller (not shown).

According to some embodiments of the present disclosure, a printedstructure 99 comprises a single device 20 disposed on a substrate 10(e.g., as shown in FIGS. 1-3) or a printed structure 99 comprisesmultiple devices 20 are disposed on a substrate 10 (e.g., as shown inFIG. 4). In either case, printed structure 99 can itself be a device 20that can then be disposed as a printed structure on another substrate 10(e.g., a backplane). Thus, printed structures 99 can be employedmultiple times at different levels in micro-electronic systems. Forexample, a printed structure 99 can comprise a device 20 disposed on asubstrate 10 that in turn is disposed on another, different substrate 10to make a larger printed structure 99. Hence, a micro-electronic systemaccording to embodiments of the present disclosure can comprise aprinted structure 99 that comprises another printed structure 99 thatcomprises yet another printed structure 99, at successively smallerscales and with smaller or fewer components. Each printed structure 99can be or include a device 20 that is comprised in another, largerprinted structure 99.

As shown in FIG. 13, a printed structure 99 comprises three devices 20disposed on a common substrate 10. For example, the three devices 20 canbe three different micro-LEDs, each emitting a different color of lightdisposed on a pixel substrate 64. Printed structure 99 can therefore bea pixel 60. In some embodiments, pixel substrate 64 can be asemiconductor substrate (e.g., a silicon substrate) that comprises apixel control circuit 66 (e.g., a CMOS circuit) that controls LEDdevices 20. In some embodiments a separate control circuit with aseparate substrate (e.g., an integrated circuit) is transfer printedonto pixel substrate 64, 10 (not shown).

According to some embodiments of the present disclosure, each of theprinted structures 99 of FIG. 13 can be a device 20 that is, in turn,printed onto a substrate 10, for example a display substrate 62 to makea display 50, as shown in FIGS. 14 and 15. FIG. 15 is a plan view ofdisplay 50 having pixels 60, each pixel 60 a printed structure 99 asshown in FIG. 13. As shown in FIGS. 13 and 14, each pixel 60 (comprisingthree devices 20) comprises a pixel substrate 64 and forms a printedstructure 99. Four device electrical contacts 22 electrically connect todisplay substrate 62, 10 to form another, larger printed structure 99.Conductors 12 corresponding to a row wire 56, power wire 57, column wire58, and ground wire 59, conduct electrical signals to control each pixel60, as shown in FIG. 15. FIGS. 14 and 15 thus illustrate a display 50comprising a printed structure 99 having a substrate 10 (displaysubstrate 62) and devices 20 (each a printed structure 99 correspondingto FIG. 13).

Therefore, according to embodiments of the present disclosure, asubstrate 10 of a printed structure 99 can be an intermediate substrate64 (e.g., pixel substrate 64) and printed structure 99 can furthercomprise a system substrate 62 (e.g., a display substrate 62) comprisingsubstrate conductors 12 disposed on or in system substrate 62. Device 20can be electrically connected to substrate conductors 12 through contactelectrical conductors 34 of substrate electrical contacts 30. Anintermediate substrate 64 can be originally formed or disposed on asource wafer (e.g., a pixel source wafer) and then printed to a largersubstrate 10, such as a backplane or printed circuit board. For example,a dense array of printed structures 99 can be assembled on anintermediate source substrate and printed to a larger substrate (e.g., abackplane) in an array (e.g., having a lower areal density) to form adisplay or detector.

Embodiments of the present disclosure provide a mechanically bonded andelectrically connected device 20 and substrate 10 at a high resolutionthat does not rely on solder bumping (e.g., at a lower resolution thanprinted structures 99) or that is solder free. It can be difficult toform small, micro-sized solder structures (e.g., solder bumps). Typicalsolder bumps have a size no less than 100 microns and, in recent,advanced solder systems, have a size no less than 30 microns indiameter. In contrast, according to embodiments of the presentdisclosure, electrical connections on the order of 1-5 microns (orsmaller) are readily, efficiently, and effectively constructed with goodelectrical connection in high-volume processes and electricallyconnected to devices 20 with lengths and widths in the tens of microns(or smaller or larger). Moreover, forming rounded substrate electricalcontacts 30 as disclosed in various embodiments herein can be lessexpensive (e.g., due to reduced processing steps and/or reduced materialcosts) than alternative methods of forming robust electricalconnections, such as using devices with connection posts (e.g., asdisclosed in U.S. Patent Application Ser. No. 14/822,864). For example,due to relatively lower photolithographic resolution requirements andthe relative inexpensiveness of compliant, flexible, or reflowablepolymers, it can be easier to form rounded polymer shapes coated withelectrically conductive material than to form a connection post. In someembodiments, device electrical contacts 22 include connection posts.

Micro-transfer printing processes and structures suitable for disposingdevices 20 onto substrates 10 are described in Inorganic light-emittingdiode displays using micro-transfer printing (Journal of the Society forInformation Display, 2017, DOI # 10.1002/jsid.610,1071-0922/17/2510-0610, pages 589-609), U.S. Pat. No. 8,722,458 entitledOptical Systems Fabricated by Printing-Based Assembly, U.S. patentapplication Ser. No. 15/461,703 entitled Pressure-Activated ElectricalInterconnection by Micro-Transfer Printing, U.S. Pat. No. 8,889,485entitled Methods for Surface Attachment of Flipped Active Components,U.S. patent application Ser. No. 14/822,864 entitled Chiplets withConnection Posts, U.S. patent application Ser. No. 14/743,788 entitledMicro-Assembled LED Displays and Lighting Elements, and U.S. Pat. No.10,153,256, entitled Micro-Transfer Printable Electronic Component, thedisclosure of each of which is incorporated herein by reference in itsentirety.

For a discussion of micro-transfer printing techniques, see also U.S.Pat. Nos. 7,622,367 and 8,506,867, each of which is hereby incorporatedby reference in its entirety. Micro-transfer printing using compoundmicro-assembly structures and methods can also be used with the presentdisclosure, for example, as described in U.S. patent application Ser.No. 14/822,868, filed Aug. 10, 2015, entitled Compound Micro-AssemblyStrategies and Devices, which is hereby also incorporated by referencein its entirety. In some embodiments, micro-transfer printed structure99 is a compound micro-assembled structure (e.g., a macro-system).

Devices 20, in certain embodiments, can be made using integrated circuitphotolithographic techniques having a relatively high resolution andcost and substrates 10, for example a printed circuit board, can be madeusing printed circuit board techniques having a relatively lowresolution and cost, thereby reducing manufacturing costs.

In certain embodiments, substrate 10 comprises a member selected fromthe group consisting of polymer, plastic, resin, polyimide, PEN, PET,metal, metal foil, glass, a semiconductor, a compound semiconductor, andsapphire. In certain embodiments, substrate 10 has a thickness from 5microns to 20 mm (e.g., 5 to 10 microns, 10 to 50 microns, 50 to 100microns, 100 to 200 microns, 200 to 500 microns, 500 microns to 0.5 mm,0.5 to 1 mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10 mm to 20 mm).

Devices 20, in certain embodiments, can be constructed using foundryfabrication processes used in the art. Layers of materials can be used,including materials such as semiconductors, doped semiconductors,metals, oxides, nitrides and other materials used in theintegrated-circuit art. Each device 20 can be or include a completesemiconductor integrated circuit and can include, for example, one ormore of a transistor, a diode, a light-emitting diode, and a sensor.Devices 20 can have different sizes, for example, 50 square microns orlarger, 100 square microns or larger, 1000 square microns, larger or10,000 square microns or larger, 100,000 square microns or larger, or 1square mm or larger. Devices 20 can have variable aspect ratios, forexample between 1:1 and 10:1 (e.g., 1:1, 2:1, 5:1, or 10:1). Devices 20can be rectangular or can have other shapes.

In some embodiments, transferring, printing, or transfer printing occursby micro-transfer-printing. In some embodiments, micro-transfer printinginvolves using a transfer device (e.g., an elastomeric stamp, such as aPDMS stamp) to transfer a device 20 using controlled adhesion. Forexample, an exemplary transfer device can use kinetic or shear-assistedcontrol of adhesion between a transfer device and device 20. It iscontemplated that, in certain embodiments, where a method is describedas including micro-transfer-printing a device 20, other analogousembodiments exist using a different transfer method. In some examples,transferring a device 20 (e.g., from a source wafer to a substrate 10)can be accomplished using any one or more of a variety of knowntechniques. For example, in certain embodiments, a pick-and-place methodcan be used. As another example, in certain embodiments, a flip-chipmethod can be used (e.g., involving a handle or carrier substrate). Inmethods according to certain embodiments, a vacuum tool, electrostaticpick-up tool, or other transfer device is used to transfer a device 20.

As is understood by those skilled in the art, the terms “over” and“under” are relative terms and can be interchanged in reference todifferent orientations of the layers, elements, and substrates includedin the present disclosure. Furthermore, a first layer “on” a secondlayer is a relative orientation of the first layer to the second layerthat does not preclude additional layers being disposed therebetween.For example, a first layer on a second layer, in some implementations,means a first layer directly on and in contact with a second layer. Inother implementations, a first layer on a second layer includes a firstlayer and a second layer with another layer therebetween (e.g., and inmutual contact).

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously.

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific elements, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus andsystems of the disclosed technology that consist essentially of, orconsist of, the recited elements, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps. It is contemplated thatstructures, devices, methods, and processes of the disclosure encompassvariations and adaptations developed using information from theembodiments described herein. Adaptation and/or modification of thedevices, methods, and processes described herein may be performed bythose of ordinary skill in the relevant art.

Certain embodiments of the present disclosure are described above. Itis, however, expressly noted that the present disclosure is not limitedto those embodiments, but rather the intention is that additions andmodifications to what was expressly described in the present disclosureare also included within the scope of the disclosure. Moreover, it is tobe understood that the features of the various embodiments described inthe present disclosure were not mutually exclusive and can exist invarious combinations and permutations, even if such combinations orpermutations were not made express, without departing from the spiritand scope of the disclosure. Having described certain implementations ofstructures and methods for electrically connecting printed horizontaldevices, it will now become apparent to one of skill in the art thatother implementations incorporating the concepts of the disclosure maybe used. Therefore, the disclosure should not be limited to certainimplementations, but rather should be limited only by the spirit andscope of the following claims.

PARTS LIST

10 substrate

11 surface

12 substrate conductor/wire

16 planar electrical contact

20 device

22 device electrical contacts

23 common side

24 dielectric structure

25 second side

26 device tether

30 substrate electrical contact

31 polymer

32 contact non-conductive core/contact polymer core

33 electrical conductor coating

34 contact electrical conductor

35 diameter

36 height

38 separation distance

40 adhesive

50 display

52 row controller

54 column controller

56 row wire

57 power wire

58 column wire

59 ground wire

60 pixel

62 display substrate/system substrate

64 pixel substrate/intermediate substrate

66 pixel control circuit

70 bus

80 heat

99 printed structure

100 provide substrate step

110 coat substrate with polymer step

120 pattern polymer step

130 reflow patterned polymer step

140 coat substrate with electrical conductor step

150 pattern electrical conductor step

160 coat substrate with adhesive layer step

162 coat substrate with thin adhesive layer step

164 coat substrate with thick adhesive layer step

166 partial cure adhesive layer step

168 pattern adhesive layer step

170 provide device step

180 transfer print device step

190 cure adhesive step

192 reflow adhesive step

194 optional reflow electrical conductor step

1-32. (canceled)
 33. A method of making electrical connectionscomprising: providing a substrate comprising substrate electricalcontacts disposed on a surface of the substrate, wherein at least one ofthe substrate electrical contacts has a rounded shape; providing adevice comprising device electrical contacts disposed on a common sideof the device; and printing the device to the destination substrate suchthat each of the device electrical contacts is in electrical contactwith one of the substrate electrical contacts.
 34. The method of claim33, wherein providing the substrate comprising substrate electricalcontacts disposed on a surface of the destination substrate comprises:providing a substrate; patterning a polymer on the substrate; heatingthe patterned polymer to form one or more rounded shapes of the polymer;and coating the one or more rounded shapes with a conductive material,wherein each of the at least one of the substrate electrical contactscomprises one of the one or more rounded shapes coated with theconductive material to form a conductive surface layer that is a contactelectrical conductor.
 35. The method of claim 34, wherein coating theone or more rounded shapes with the conductive material comprises:depositing a layer of the conductive material; and patterning the layersuch that the one or more rounded shapes remain coated with theconductive material.
 36. The method of claim 33, comprising disposingadhesive on the destination substrate prior to printing the device,wherein printing the device comprises contacting the device to theadhesive.
 37. The method of claim 36, comprising curing the adhesiveafter the device has been printed.
 38. The method of claim 33,comprising baking the device and the destination substrate.
 39. Themethod of claim 33, comprising reflowing the conductive material. 40.The method of claim 33, comprising reflowing the rounded shape.
 41. Themethod of claim 33, comprising conforming the substrate electricalcontact to the device electrical contact.
 42. The method of claim 33,wherein the at least one of the substrate electrical contacts comprisesa polymer core disposed on the surface of the substrate, the polymercore is coated with a contact electrical conductor on a surface of thepolymer core, wherein the surface of substrate has a surface energysufficient to reflow the polymer core into the rounded shape when thepolymer core has been heated, and wherein the polymer core is a reflowedbead, wherein each of the at least one of the substrate electricalcontacts has a lateral extent over the substrate of no more than 10 μmand the device comprises a fractured or separated device tether.
 43. Themethod of claim 33, wherein the device electrical contacts aresubstantially planar and are disposed in a common plane.
 44. The methodof claim 33, wherein the device electrical contacts are substantiallyplanar and are disposed in different planes.
 45. The method of claim 33,wherein the polymer core is compliant, conformal, or flexible.
 46. Themethod of claim 33, wherein the polymer core comprises an electricallyconductive polymer.
 47. The method of claim 33, wherein the contactelectrical conductor is reflowable.
 48. The method of claim 33, whereinthe contact electrical conductor has been wicked along the deviceelectrical contact.
 49. The method of claim 33, wherein the device istilted with respect to the substrate.
 50. The method of claim 33,comprising an adhesive disposed between the device and the substratethat adheres the device to the substrate.
 51. The method of claim 33,wherein the at least one of the substrate electrical contacts is aplurality of the substrate electrical contacts and the pluralitycomprises ones of the substrate electrical contacts having differentheights or sizes.
 52. The method of claim 33, wherein the device is anunpackaged bare die.